The subject invention relates to a new and improved drive system which is particularly adapted for use in ships which includes a main driving engine having high efficiency at low power, in combination with a high power gas turbine engine. In accordance with the subject invention, the total power output generated by the engine combination is increased by using the main driving engine to run a compressor for supercharging the gas turbine engine. The resulting power generated by the supercharged gas turbine engine is greater than the sum of the powers generated by the turbine and main driving engines individually.
In the prior art, the selection of a drive system for a particular craft is dependent on various factors such as efficiency and power requirements, as well as the relative size and weight of the drive system and craft. In combat vehicles such as tanks, ships, and more specifically, patrol boats, it is desirable to provide a drive system which is both fuel efficient at low power, for long range cruising operations, and also capable of generating high power for short periods of time. More specifically, a patrol boat is generally required to spend a significant amount of time cruising at low speeds, on the order of 15 knots. Since a patrol boat is often away from its base for weeks at a time, a main engine drive which is efficient at low power is necessary. Typically, a large diesel engine, which may weight up to ten tons, is selected since it is fuel efficient at low power, and weight is not a critical restrictive factor on a ship. In the alternative, a small gas turbine engine is used for cruising speeds. As can be appreciated, however, situations arise when the patrol boat must travel at considerably higher speeds, on the order of 40 to 50 knots. An additional engine is required which can produce power 3 to 5 times greater than the diesel engine. To satisfy the latter requirements, a high power gas turbine engine is usually chosen. While a gas turbine engine is inefficient at low power outputs, it can generate the high power output necessary for combat conditions.
Accordingly, in the prior art, patrol boats have been provided with drive system combinations which include both a main driving diesel engine and a high power gas turbine engine. One example of this type of prior art combination drive system, as used in ships, can be found in U.S. Pat. No. 3,826,218, issued July 30, 1974 to Hiersig et al.
The prior art combination drive systems generally fall into two main catagories. The first is the Combined Diesel or Gas Turbine Engine System identified by the acronym "CODOG" which is designed such that power is transmitted to the propeller shaft by either the diesel engine or the gas turbine engine. More specifically, coupling arrangements are provided such that at slow cruising speed, the fuel efficient diesel engine is coupled to the propeller shaft, while the gas turbine engine is disengaged. In contrast, when high power is required for combat speeds, the diesel engine is disengaged from the propeller shaft and the gas turbine engine is coupled thereto instead. As can be appreciated, the maximum power which may be delivered to the shaft, at one time in a CODOG system, is equivalent to the maximum power output of the gas turbine engine.
In order to increase the maximum power output delivered to the shaft, an improved system was developed in the prior art called the Combined Diesel and Gas Turbine Engine System, identified by the acronym CODAG. In the latter CODAG systems, low cruising speeds are obtained by coupling only the fuel efficient diesel engine to the shaft. At higher speeds, the diesel engine is disengaged from the shaft, and the gas turbine engine is coupled thereto instead. Thus, at low and middle speed ranges the CODAG system resembles the CODOG system. However, when maximum combat speed is required in the CODAG system, the output of both the diesel and the gas turbine engines are coupled to the propeller shaft. By this arrangement, the maximum total power which is delivered to the shaft is equal to the sum of the horsepower generated by both the diesel and the gas turbine engines. Thus, compared to the CODOG system, where the maximum power which can be delivered to the shaft is equal to the power output of the gas turbine engine, a CODAG drive system permits the output of both engines to be coupled to the shaft simultaneously.
Other similar systems have been developed wherein both engines are gas turbines, with the main driving turbine being considerably smaller than the high power turbine. The advantage of using two turbines is that a small turbine operating at maximum capability is more fuel efficient than a large unit operating at low power output. Analagous drive systems have been developed wherein either or both engines can be coupled to the output shaft and are identified by the acronyms COGOG and COGAG, respectively.
In order to achieve the coupling of both engines to the shaft in a CODAG or COGAG system, it is necessary to provide a complex gearing and clutch arrangement. More particularly, a major shortcoming of the combined systems is that since the main driving and gas turbine engines operate in a different manner, at different speeds, sophisticated, synchronized linkage arrangements are required to simultaneously couple both engine outputs to the drive shaft. One example of such a synchronized clutch arrangement can be found in the above cited U.S. Pat. No. 3,826,218. It is apparent that even with its shortcomings, the development of the prior art combined drive systems demonstrate the desirability of providing a drive system wherein power delivered to the output shaft is maximized.
Accordingly, it is an object of the subject invention to provide a new and improved drive system wherein the total horsepower delivered to the shaft is greater than the sum of the horsepower of each individual engine.
It is a further object of the subject invention to provide a new and improved drive system wherein maximum horsepower is achieved by using the main driving engine to drive a compressor for supercharging the gas turbine engine thereby boosting its horsepower output an amount greater than the output of the main driving engine alone.
It is another object of the subject invention to provide a new and improved drive system for use with a diesel and gas turbine engine combination which does not require the use of complex synchronized linkage and clutch arrangements utilized to the prior art to couple both engines to the shaft at the same time for achieving maximum power.
It is still a further object of the subject invention to provide a new and improved drive system wherein precompressed air is cooled prior to delivery to the gas turbine engine for further increasing the power output of the turbine engine.